Insects of Britain and Ireland: orders

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L. Watson and M. J. Dallwitz

Character list

#1. <Nomenclature (synonyms, alternative names, etc.):>/

~ (‘alternatively’) is here used to indicate ‘sometimes not unreasonably included in or reduced to’.

#2. <Common name(s) of members:>/

Adult insects

#3. <Whether adults terrestrial or aquatic:>/

1. terrestrial <implicit>/

2. aquatic/

#4. <Association of adults with water:>/

1. nearly always found near water <when aquatic, or when associated with helophytic plants>/

2. not particularly associated with water <implicit>/

#5. <Whether social insects:>/

1. social, constituting organized colonies/

2. not social <implicit>/

#6. <Feeding habits of ADULTS (cf. the characters describing mouthparts):>/

1. predatory/

2. phytophagous <on living plant material>/

3. imbibing nectar/

4. saprophagous <on decaying organic matter>/

5. coprophagous/

6. consuming stored produce/

7. mycophagous/

8. parasitic/

9. incapable of feeding/

Note the essential distinction to be made between “parasitic”, referring to the general life-style of a species (q.v.); and the same term when it relates, as here, to the precise feeding habits of individuals. The different concepts are often confused in entomological literature. See the character concerned with the feeding habits of larvae for further comments.

In practice, the distinction between “parasitic” and “predatory” is less clear than text-book definitions usually suggest. The larvae of many Diptera and Hymenoptera, in particular, contradict the common assertion that highly specialised parasitism does not result in the unduly premature death of the host (with the added, teleological supposition that to do so is inimical to the long term survival of the parasitic species). In fact, many dipteran and hymenopteran larvae universally described as “parasitic” are highly adapted to keep the host alive only for as long as it is needed as a source of food, before ultimately killing it.

#7. <Whether parasitic ADULTS victimize warm-blooded animals:>/

1. ectoparasitic on mammals/

2. ectoparasitic on birds/

3. parasitising invertebrates only <implicit>/

#8. <Whether the adults are ‘jumpers’ (saltatorial):>/

1. conspicuous ‘jumpers’ <saltatorial>/

2. not ‘jumpers’ <implicit>/

#9. <Whether adults emit sound:>/

1. voluntarily emitting sound <by stridulation or other special mechanisms, and excluding flight-related buzzing, humming, etc.>/

2. mute/

#10. <Size of adult insect, excluding antennae and abdominal appendages:>/

1. minute <less than 3mm long>/

2. small <3–15 mm long>/

3. medium sized <15–25 mm long>/

4. large <25–40 mm long>/

5. very large <i.e., by the standards of British insects: more than 40 mm long>/

#11. <Adults, presence of elytra>/

1. with hardened ‘elytra’ (q.v.), representing the fore-wings/

2. without elytra/

#12. <Adults, whether flying or flightless:>/

1. capable of flight <wings conspicuous, and at least one pair functional for flight>/

2. flightless <wingless, or wings all much reduced and not functioning directly for flight>/

#13. <Flying adults: number of membranous propellant wings>/

1. with one pair of <membranous> propellant wings/

2. with two pairs of <membranous> propellant wings/

#14. Body <plane of flattening>/

1. dorsiventrally flattened/

2. more or less cylindrical/

3. laterally flattened/

#15. Head <hypognathy>/

1. prognathous/

2. hypognathous/

3. opisthognathous/

‘Gnathy’ refers to the inclination of the long axis of the head, and the position of the mouthparts, relative to the long axis of the body.

‘Prognathous’: head aligned more or less horizontally with the long axis of the body, the mouthparts more or less anterior.

‘Hypognathous’: long axis of the head more or less vertical, the mouthparts more or less ventral (the common condition).

‘Opisthognathous’: head inclined beyond the vertical against the body, so that the ‘chin’ recedes (an uncommon state).

#16. Head <whether prolonged into a beak>/

1. prolonged into a rigid beak <rostrum>/

2. not rigidly beaked <implicit>/

#17. Mouthparts <feeding-related components, well developed or reduced>/

1. well developed <relative to the 'generalized biting type' (q.v.): most of the components readily recognizable, or the mouthparts with evident feeding-related modifications>/

2. much reduced <relative to the 'generalized biting type': all the feeding-related components much reduced or missing>/

For more details on the interpretations of insect mouthparts, see the Notes attached to the character concerned with whether the ‘trophi’ are of generalized or highly specialized type.

The following terminology relates the diversity of insect mouthparts to the ‘generalized biting type’, represented on the illustration by those of a beetle (Dytiscus, ventral view of the right side of the head). See also the diagrams accessible via the ‘Insect morphology’ toolbar button.

The LABRUM (upper lip) is a single, sclerotized plate, hinged on the adjoining part (clypeus) of the rigid head capsule, overlying the opening of the mouth and the bases of the other mouthparts. Its inner surface has gustatory functions, and in Hymenoptera it bears a small lobe (the epipharynx), which assumes impressive proportions as the ‘epipharyngeal stylet’ in the fleas.

The two MANDIBLES (jaws, concerned with biting and chewing) lie over the mouth, and articulate at the sides of the rigid head capsule. They are always relatively simple and unsegmented, although they are sometimes much modified in size and form. They may represent the bases of a pair of ancestral limbs.

The HYPOPHARYNX is an unpaired, medial, tongue-like organ, arising from the floor of the mouth and projecting from between the oral cavity and the labium. It is inconspicuous in mouthparts of the generalized type, but is highly developed in some groups.

The MAXILLAE (lower, accessory jaws) are relatively complex, with a principal axis comprising an articulating basal segment (the cardo), and a main axial segment (the stipes), the latter bearing a segmented (sensory) maxillary palp, an axial maxillary lobe (the lacinia), and a lateral lobe (the galea).

The bilaterally symmetrical LABIUM, functioning as the lower lip, represents a second pair of maxillae that have become fused in the course of evolution. It exhibits a mentum and a prementum (representing fused cardo and stipes of the maxillae); and more distally on each side, a medial glossa (representing the maxillary lacinia), a paraglossa (outside it, representing the maxillary galea), and a labial palp. Differing extents of fusion of the components of the labium are exhibited among the insect Orders, as exemplified in the accompanying images.

#18. Mouthparts <whether functional for feeding>/

1. functional for feeding <implicit>/

2. non-functional for feeding/

#19. Mouthparts <type>/

1. of the biting type <exhibiting recognisable, operational mandibles>/

2. suctorial/

3. adapted for both biting and sucking/

#20. Mouthparts <whether piercing>/

1. piercing/

2. not piercing/

#21. Mouthparts <‘trophi’, whether of generalized biting or highly specialized type: see Notes for general discussion and morphological interpretation of insect mouthparts>/

1. <more or less> conforming to the generalized biting type/

2. highly modified <from the generalized biting type: specify how>/

The ‘generalized biting type’ is adequately exemplified in the accompanying illustrations by the mouthparts of Dytiscus, but some insect Orders exhibit or are characterised by spectacular modifications associated with different life-styles and feeding habits: modifications involving fusion of components, reduction or loss of some, and/or major re-shaping of others. For the present purpose, we are adopting the convenient and helpful standard practice of categorizing the diversity of insect mouthparts with reference to the structures identifiable in the ‘generalized biting’ type.

Comparative morphological and phylogenetic interpretation of the enormous range of known insects show that they can all be plausibly derived from a myriapodan ancestral form exhibiting twenty similar segments, by invoking co-ordination and/or amalgamation of segments and their paired appendages to perform related functions. Hence the head reflects adaptations for sensory perceptions and feeding. It seems to represent three pre-oral segments (bearing the antennae and the eyes), followed by three fused, appendage-bearing segments constituting the mouthparts. The latter are flagged in sequence by their paired appendages; viz., the mandibles (over the oral cavity, and articulating immediately behind the labrum); the maxillae (which afford more evidence of phylogenetic derivation from walking legs); and the labium, apparently representing a second pair of maxillae that have usually become fused into single structure, but incomplete fusion attesting to its dual origin can be seen in some Orders.

The standard interpretations of mouthparts components in the accompanying illustrations may suggest outrageous phylogenetic theorizing when presented without the underlying evidence from comparative morphology and world-wide sampling, but they are in fact well substantiated. Furthermore, students of the history of science should realize that the principal descriptive terms, the comparative morphological concepts, and the main classificatory conclusions derived from contemplating insect mouthparts, although presented in overtly phylogenetic terms in modern textbooks, were originally formulated without resort to evolutionary considerations. The taxonomic practices of late Eighteenth and early Nineteenth Century entomologists were apparently uninfluenced by the evolutionary insights of Lamarck, and their classificatory legacy has remained largely impervious to Darwin's subsequent, more influential exposition. The realization of the truth of evolution represented a major advance in human thought (giving rise, for example, to the science of genetics); but it is a popular fallacy that the concept had a revolutionary effect on taxonomic practice. In fact, it was the inevitable consequence of contemplating the taxonomic facts set out so elegantly in the works of early taxonomists, exemplified here by John Curtis’s British Entomology.

The following terminology relates the diversity of insect mouthparts to the ‘generalized biting type’, represented on the illustration by those of a beetle (Dytiscus, ventral view of the right side of the head). See also the diagrams accessible via the ‘Insect morphology’ toolbar button.

The LABRUM (upper lip) is a single, sclerotized plate, hinged on the adjoining part (clypeus) of the rigid head capsule, overlying the opening of the mouth and the bases of the other mouthparts. Its inner surface has gustatory functions, and in Hymenoptera it bears a small lobe (the epipharynx), which assumes impressive proportions as the ‘epipharyngeal stylet’ in the fleas.

The two MANDIBLES (jaws, concerned with biting and chewing) lie over the mouth, and articulate at the sides of the rigid head capsule. They are always relatively simple and unsegmented, although they are sometimes much modified in size and form. They may represent the bases of a pair of ancestral limbs.

The HYPOPHARYNX is an unpaired, medial, tongue-like organ, arising from the floor of the mouth and projecting from between the oral cavity and the labium. It is inconspicuous in mouthparts of the generalized type, but is highly developed in some groups.

The MAXILLAE (lower, accessory jaws) are relatively complex, with a principal axis comprising an articulating basal segment (the cardo), and a main axial segment (the stipes), the latter bearing a segmented (sensory) maxillary palp , an axial maxillary lobe (the lacinia), and a lateral lobe (the galea).

The bilaterally symmetrical LABIUM, functioning as the lower lip, represents a second pair of maxillae that have become fused in the course of evolution. It exhibits a mentum and a prementum (representing fused cardo and stipes of the maxillae); and more distally on each side, a medial glossa (representing the maxillary lacinia), a paraglossa (outside it, representing the maxillary galea), and a labial palp. Differing extents of fusion of the components of the labium are exhibited among the insect Orders, as exemplified in the accompanying images.

#22. The clypeus <of adults, form>/

1. divided into a narrow, transverse anteclypeus and a characteristically bulbous postclypeous/

2. not transversely divided and bulbous above as in Psocoptera (q.v.)/

#23. Antennae <present or absent>/

1. present <implicit>/

2. absent/

#24. Antennae <whether conspicuous>/

1. conspicuous <large or long>/

2. inconspicuous <small and short>/

#25. Antennae <simple or complex>/

1. simple/

2. complex/

#26. Antennae <number of segments>/

segmented/

#27. Compound eyes <present or absent>/

1. present and well developed <implicit>/

2. vestigial or absent/

Specialized inhabitants of dark habitats, with the compound eyes vestigial or lacking, are recorded from other parts of the world for several Orders - notably from Hymenoptera (a few ants), Dermaptera, and Hemiptera - which, in the absence of evidence to the contrary, are tentatively assumed to universally exhibit them in Britain.

#28. Ocelli <number>/

#29. Wings <ostensible number>/

1. two <including forms where one pair is represented by vestigial structures>/

2. four <including forms with fore-wings represented by wing-cases or elytra>/

#30. The single pair <of wings, when ostensibly one pair only, texture>/

1. membranous/

2. leathery/

3. horny/

#31. Hind-wings <whether represented by halteres>/

1. <vestigial and> represented by small, clubbed ‘halteres’/

2. not represented by halteres <implicit>/

#32. Wings <when four, whether both pairs similar in texture>/

1. of similar texture in both pairs/

2. markedly differently textured in the two pairs/

#33. Fore-wings <of 4-winged insects, texture>/

1. membranous/

2. leathery/

3. basally leathery, distally membranous/

4. horny/

#34. Fore-wings <presence of pterostigma>/

1. with a pterostigma/

2. without a pterostigma/

#35. Hind-wings <size relative to that of the fore-wings>/

1. smaller <in area> than the fore-wings/

2. similar in size to the fore-wings/

3. larger <in area> than the fore-wings/

#36. Hind-wings <breadth relative to fore-wings>/

1. markedly broader than the fore-wings/

2. no broader than the fore-wings/

#37. Hind-wings <whether folded in the resting insect>/

1. folded in repose/

2. not folded in the resting insect/

#38. Wings <venation>/

1. with numerous cross-veins <reticulate venation>/

2. with <relatively> few cross-veins/

#39. Wings <vestiture>/

1. conspicuously hairy/

2. conspicuously scaly/

3. more or less naked <neither conspicuously hairy nor scaly>/

#40. Wings <presence of ‘corneous dots’>/

1. exhibiting ‘corneous dots’ <one distally near the base of vein fork 2 of each fore-wing, often one also in the corresponding position in the hind-wings, and sometimes another in the thyridial cell proximal to the centre of the fore-wing as well>/

2. without ‘corneous dots’ <implicit>/

‘Corneous dots’ (nygmata, thyridia): small, thickened, chitinous (usually semi-transparent, whitish) spots, of almost universal occurrence in Trichoptera, and said by Riek (1970) to be common also in Neuroptera. “Possibly due to presence of a gland or sensory organ” (Imms, 1957).

#41. Wings <fringing>/

1. fringed/

2. not fringed/

#42. Wings of the resting insect <carriage>/

1. held above the body, with their upper surfaces more or less apposed/

2. <more or less> outspread/

3. closed and directed backwards/

#43. Wings of the resting insect <whether held flat or roof-like over the abdomen>/

1. held roof-like over the abdomen <with the hind margin uppermost>/

2. not held roof-like /

#44. Thoracic legs <of adults>/

1. present <implicit>/

2. absent/

#45. The body and legs of wingless adults <whether scaly>/

1. bearing <lepidopteran> scales/

2. without scales <implicit>/

#46. Tarsi <reduction>/

1. reduced to pretarsal claws terminating the tibiae /

2. not completely reduced to pretarsal claws <implicit>/

#47. Tarsi <number of segments>/

segmented/

Where the number of tarsi is known to differ in fore-, mid- and hind-legs, the data in this data set are intended to be inclusive. In using the character for identification, however, while it should suffice to enter a count for one leg, it would be safer to enter an observed range.

#48. Abdomen <whether conspicuously appendaged>/

1. <more or less> conspicuously appendaged at the rear/

2. not conspicuously appendaged/

#49. Abdomen <spectacular appendages>/

1. furnished with very large, paired, pincer-like appendages <modified cerci>/

2. exhibiting a conspicuous ovipositor/

3. with <two or three> long terminal bristles <‘styles’>/

4. not spectacularly appendaged <without pincer-like appendages, with no conspicuous ovipositor, without terminal long bristles> <implicit>/

#50. Abdomen <visibility of cerci>/

1. with cerci clearly visible at its tip/

2. lacking clearly visible cerci/

‘Cerci’: paired appendages on the 11th abdominal segment, which when present vary from short bristles to elongated, tenuous filaments to large ‘pincers’.

#51. Abdomen of females <whether with an exserted ovipositor>/

1. with an exserted ovipositor/

2. with no exserted ovipositor/

#52. Abdomen apparently <number of externally detectable segments>/

segmented/

#53. Abdomen <of adults, presence of rudimentary abdominal limbs>/

1. exhibiting rudimentary abdominal limbs/

2. with no rudimentary abdominal limbs <implicit>/

Eggs

#54. The eggs <whether eggs in oothecae>/

1. laid in batches within a protective case (ootheca)/

2. not laid in batches within a protective case (ootheca) <implicit>/

Larvae

#55. Larvae <terrestrial or aquatic>/

1. terrestrial <implicit>/

2. aquatic/

#56. Larvae <habits>/

1. feeding in the open/

2. clandestine feeders/

#57. Larvae <feeding habits of larvae>/

1. predatory/

2. phytophagous <feeding on living plant material>/

3. saprophagous <feeding on decaying organic matter>/

4. coprophagous/

5. consuming stored produce/

6. mycophagous/

7. parasitic/

8. feeding on food gathered and stored by the adults/

Note the essential distinction to be made between “parasitic”, referring to the general life-style of a species (q.v.); and the same term when it relates, as here, to the precise feeding habits of individuals. The different concepts are often confused in entomological literature.

In practice, the distinction between “parasitic” and “predatory” is less clear than text-book definitions usually suggest. The larvae of many Diptera and Hymenoptera, in particular, contradict the common assertion that highly specialised parasitism does not result in the unduly premature death of the host (with the added, teleological supposition that to do so is inimical to the long term survival of the parasitic species). In fact, many dipteran and hymenopteran larvae universally described as “parasitic” are highly adapted to keep the host alive only for as long as it is needed as a source of food, before ultimately killing it.

#58. Larvae <presence of segmented thoracic legs>/

1. with three pairs of segmented thoracic legs/

2. without segmented thoracic legs/

#59. Larvae <presence of ventral abdominal prolegs>/

1. with ventral abdominal prolegs/

2. without ventral abdominal prolegs/

#60. Larvae <presence of anal prolegs>/

1. with paired anal prolegs <claspers>/

2. without anal prolegs/

#61. The abdominal prolegs <whether bearing crochets>/

1. bearing crochets/

2. without crochets/

#62. Larvae <whether strongly pigmented>/

1. brightly coloured/

2. drab <pallid, whitish, grey, brown, etc.: implicit>/

#63. Larval head <presence of sclerotized head capsule>/

1. with a well sclerotized capsule/

2. without a well sclerotized capsule/

#64. Development of larva into adult <gradual or involving discontinuous change>/

1. gradual/

2. involving marked metamorphosis/

#65. Development of larva into adult <endopterygote/exopterygote>/

1. endopterygote <wings developing internally, only becoming apparent when they are fully developed and the insect emerges from its final moult>/

2. exopterygote <the wings gradually developing externally as the insect grows>/

3. apterygote <wings absent>/

#66. Development of larva into adult <whether involving a quiescent, pupal stage>/

1. involving a <quiescent> pupal stage <immediately prior to emergence of the adult insect>/

2. not involving a pupal stage/

Pupae

#67. Pupae <whether in a puparium>/

1. in a puparium/

2. without a puparium/

‘Puparium’: a persistent, hardened and modified, usually barrel-shaped, ovoid or globular derivative of the cuticle of the third larval instar, functioning as a cocoon enclosing a thin-skinned pupa. In a few families (e.g. Stratiomyidae), the last larval skin persists in unmodified form (‘transitional puparia’).

#68. Pupae <presence of articulated mandibles>/

1. with articulated mandibles <decticous>/

2. without articulated mandibles <adecticous>/

#69. Pupae <whether appendages free or fused to the body>/

1. with free appendages <legs, wings: exarate>/

2. with the appendages fused to the body <obtect>/

Classification

#70. Subclass/

1. Apterygota/

2. Pterygota/

#71. Division <of Pterygota>/

1. Exopterygota/

2. Endopterygota/

British representation

#72. <Families in Britain:>/

#73. Genera <number in Britain>/

#74. <Number of species in Britain>/

species/

Special features

#75. <Possession of raptorial fore-legs associated with ‘praying mantis’ posture>/

1. with conspicuously modified, raptorial fore-legs, associated with a characteristic ‘praying’ posture/

2. the fore-legs not conspicuously raptorial, the posture not ‘praying mantis-like’ <implicit>/

#78. <Peculiar features of Strepsiptera>/

1. males actively flying, having fore-wings reduced to knobbed, haltere-like structures and large, membranous hind-wings; females larviform and confined to puparia inside hymenopterous or hemipterous hosts/

2. males not having fore-wings reduced to knobbed, haltere-like structures, and the females not larviform parasites; i.e., by contrast with Strepsiptera <implicit>/

#79. The wingless adults <whether larviform>/

1. not larviform, with only obscure thoracic segmentation <readily distinguishable thorax and abdomen>/

2. larviform, with the thorax clearly segmented/

#80. The adults <peculiar features of Pthiraptera>/

1. highly specialized, very dorsoventrally flattened, blind external parasites, which spend their whole lives clinging to their hosts via their modified tarsi <Pthiraptera>/

2. not having the peculiar features of Pthiraptera/

General comments

#81. <General comments:>/

#82. <Unsatisfactorily resolved:>/

#83. <Abbreviated taxon name:>/

Miscellaneous

#84. <Illustrations:>/


To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: orders. Version: 16th May 2016. delta-intkey.com’.

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